SAN FRANCISCO — Two privacy advocacy groups urged Facebook Inc on Monday to withdraw proposed changes to its terms of service that would allow the company to share user data with recently acquired photo-application Instagram, eliminate a user voting system and loosen email restrictions within the social network.

The changes, which Facebook unveiled on Wednesday, raise privacy risks for users and violate the company’s previous commitments to its roughly 1 billion members, according to the Electronic Privacy Information Center and the Center for Digital Democracy.

“Facebook’s proposed changes implicate the user privacy and terms of a recent settlement with the Federal Trade Commission,” the groups said in a letter to Facebook Chief Executive Mark Zuckerberg that was published on their websites on Monday.

By sharing information with Instagram, the letter said, Facebook could combine user profiles, ending its practice of keeping user information on the two services separate.

Facebook declined to comment on the letter.

In April, Facebook settled privacy charges with the U.S. Federal Trade Commission that it had deceived consumers and forced them to share more personal information than they intended. Under the settlement, Facebook is required to get user consent for certain changes to its privacy settings and is subject to 20 years of independent audits.

Facebook, Google and other online companies have faced increasing scrutiny and enforcement from privacy regulators as consumers entrust ever-increasing amounts of information about their personal lives to Web services.

Facebook unveiled a variety of proposed changes to its terms of service and data use polices on Wednesday, including a move to scrap a 4-year old process that can allow the social network’s roughly 1 billion users to vote on changes to its policies.

If proposed changes generate more than 7,000 public comments during a seven-day period, Facebook’s current terms of service automatically trigger a vote by users to approve the changes. But the vote is only binding if at least 30 percent of users take part, and two prior votes never reached that threshold.

The latest proposed changes had garnered more than 17,000 comments by late Monday.

Facebook also said last week that it wanted to eliminate a setting for users to control who can contact them on the social network’s email system. The company said it planned to replace the “Who can send you Facebook messages” setting with new filters for managing incoming messages.

That change is likely to increase the amount of unwanted “spam” messages that users receive, the privacy groups warned on Monday.

Facebook’s potential information sharing with Instagram, a photo-sharing service for smartphone users that it bought in October, flows from proposed changes that would allow the company to share information between its own service and other businesses or affiliates it owns.

The change could open the door for Facebook to build unified profiles of its users that include people’s personal data from its social network and from Instagram, similar to recent moves by Google Inc.

In January, Google said it would combine users’ personal information from its various Web services – such as search, email and the Google+ social network – to provide a more customized experience. The unified data policy raised concerns among some privacy advocates and regulators, who said it was an invasion of people’s privacy.

“As our company grows, we acquire businesses that become a legal part of our organization,” Facebook spokesman Andrew Noyes said in an emailed statement on Monday.

“Those companies sometimes operate as affiliates. We wanted to clarify that we will share information with our affiliates and vice-versa, both to help improve our services and theirs, and to take advantage of storage efficiencies,” Noyes said.